The present invention generally relates to liquid crystal displays (LCDs), and more particularly relates to dual mode backlit LCDs, and even more particularly relates to methods and apparatus for backlighting LCD""s with dual modes without the use of an edge lighted or waveguide lighted backlighting scheme.
In the past, LCDs have been used in a wide variety of environments, including displays within the cockpit of an aircraft. In some aircraft it is desirable to have LCDs with dual mode backlighting. These displays have a mode for use during daylight operation and a mode for nighttime operation when a pilot is using a night vision imaging system, hereafter NVIS. It has been well known to use filtered light during the NVIS mode. Filtering the light enhances the performance of the display when NVIS equipment is used. Without other changes, the filtering which helps NVIS performance degrades the optical performance (mainly color and brightness) of the same LCD in daylight.
One example of a prior art system is shown in FIG. 1, which includes a heat sink with a plurality of light pipes therethrough disposed about a night mode array of light emitting diodes (LEDs).
While these LCD backlighting systems may have many advantages in particular uses, they also have created challenges. One common challenge created by these designs is the relatively high temperatures experienced by the day and night mode LEDs and the concomitant lower luminance, shorter life and/or increased power consumption.
Consequently, there exists a need for improved methods and apparatuses for backlighting compact dual mode LCDs.
It is an object of the present invention to provide an LCD which is highly compact.
It is another object of the present invention to provide an LCD with improved luminance and luminance uniformity.
It is yet another object of the present invention to provide an LCD with extended MTBF.
It is yet another object of the present invention to provide an LED backlight for an LCD which consumes less power.
It is a feature of the present invention to utilize a thermal path across a night mode LED array with a heat sink disposed behind the night mode LED array.
It is a feature of the present invention to package day and night mode LED arrays with reduced detriment to the main cooling structure (heat sink).
The present invention is an apparatus and method for backlighting an LCD which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features and achieve the already articulated advantages. The present invention is carried out in a xe2x80x9cwasted space-lessxe2x80x9d and xe2x80x9cwasted power-lessxe2x80x9d manner in a sense that the size of a fully functional dual mode luminare and the power consumed has been reduced.
Accordingly, the present invention is an LCD system including a predetermined sequence and orientation of backlighting LED elements which includes a day mode LED array and a separate night mode LED array where a thermal conduction path from said day mode LED array extends across the night mode LED array to a heat sink disposed behind both LED arrays.